ABSTRACT
Chitosans were obtained by room-temperature-homogeneous-deacetylation (RTHD) and freeze-pump-out-thaw-heterogeneous-deacetylation (FPT) from chitins purified from fermentations. Commercial chitosan was deacetylated by three-FPT-cycles. Chitosans and Pichia guillermondii were evaluated on the growth of Penicillium digitatum. Medium molecular weight (M(W)) chitosans displayed higher inhibitory activity against the yeast than low M(W) biopolymers. Chitosans with low degree of acetylation (DA) were inhibitory for yeast and mould. Therefore, a low M(W) and high DA chitosan was selected for use against moulds combined with yeasts. Biopolymer and yeasts presented an additive effect, since chitosans were effective to delay spore germination, whereas yeast decreased apical fungal growth.
Subject(s)
Chitosan/pharmacology , Penicillium/drug effects , Penicillium/growth & development , Pichia/chemistry , Acetylation , Chitosan/metabolism , Kinetics , Microscopy, Electron, Scanning , Molecular Weight , Penicillium/ultrastructure , Spores, Fungal/drug effects , Spores, Fungal/growth & developmentABSTRACT
Fermentation bioprocesses typically involve two liquid phases (i.e. water and organic compounds) and one gas phase (air), together with suspended solids (i.e. biomass), which are the components to be dispersed. Characterization of multiphase dispersions is required as it determines mass transfer efficiency and bioreactor homogeneity. It is also needed for the appropriate design of contacting equipment, helping in establishing optimum operational conditions. This work describes the development of image analysis based techniques with advantages (in terms of data acquisition and processing), for the characterization of oil drops and bubble diameters in complex simulated fermentation broths. The system consists of fully digital acquisition of in situ images obtained from the inside of a mixing tank using a CCD camera synchronized with a stroboscopic light source, which are processed with a versatile commercial software. To improve the automation of particle recognition and counting, the Hough transform (HT) was used, so bubbles and oil drops were automatically detected and the processing time was reduced by 55% without losing accuracy with respect to a fully manual analysis. The system has been used for the detailed characterization of a number of operational conditions, including oil content, biomass morphology, presence of surfactants (such as proteins) and viscosity of the aqueous phase.
Subject(s)
Bacteria/cytology , Bioreactors/microbiology , Cell Culture Techniques/methods , Culture Media/analysis , Image Interpretation, Computer-Assisted/methods , Microscopy, Video/methods , Nephelometry and Turbidimetry/methods , Bacteria/isolation & purification , Cell Culture Techniques/instrumentation , Equipment Design , Equipment Failure Analysis , Image Interpretation, Computer-Assisted/instrumentation , Microscopy, Video/instrumentation , Nephelometry and Turbidimetry/instrumentation , Phase Transition , ViscosityABSTRACT
Image analysis was used to measure the effect of Tween 40 on the morphology of Trichoderma harzianum. The percentage of pellets was maximal (93%) with Tween at 0.2 ml l(-1), whereas the maximal proportion of dispersed mycelia (40%) was with Tween at 1.6 ml l(-1). The particle median diameter decreased from 2 to 0.5 mm as Tween concentration was increased and was inversely correlated to the biomass dry weight. Adding pre-determined aliquots of Tween 40 to the culture medium can be used to define the morphological characteristics of Trichoderma harzianum in submerged shake-flask culture.
